1. Field
The present invention relates generally to weapon systems and methods, and more particularly to weapon systems and methods for beam containment and beamwalk maintenance utilizing optical fibers.
2. Background
Currently, the state-of-the-art approach to the problem of line-of-sight beam alignment for airborne laser systems is various active beamwalk alignment or maintenance systems that comprise a set of active beamwalk mirrors controlled by complicated electro-servo mechanisms. FIG. 1 illustrates one such beamwalk maintenance system for an Airborne Laser System. As shown in FIG. 1, the beams of a high power Track Illuminator (TILL) laser (110) and of a high power Beacon Illuminator (BILL) laser (120) are sent from the Multi-Beam Illuminator (MBIL) Bench (130) to the Beam Transfer Assembly (BTA) Bench (140) in a stable fashion. The two benches have considerable separation, and the benches tilt relative to each other. The beamwalk maintenance system shown in FIG. 1 employs active or movable Beamwalk Mirrors (BWM's) to maintain line-of-sight beam alignment for TILL and BILL lasers despite the relative movement of the optical benches. A pair of Beamwalk Mirrors (BWM's) are used for each laser—BWMs #5 and #6 for the BILL, and BWMs #7 and #8 for the TILL laser. To describe briefly, the first BWM of each pair tilts to center their beams onto the second mirrors, and the second mirrors then tilt to adjust the directions of the beams leaving them so that they center on the steering mirrors. The mirrors are actuated by voice-coil servo mechanism with control electronics. The control signals for these voice-coil-driven BMWs are derived from the beam walk sensors (160) which are sensitive to the centroids and angular directions of the beams coming from the beamwalk laser source (170) that are back-propagated through the same mirror systems. Thus, if any of the illuminator beams wander or “walk” off-center at the steering mirrors, the beamwalk laser beams arriving at the beamwalk sensors (160) also fall off-center, producing feedback signals, which are then processed by a processor to generate the control signals to the voice-coil-driven BMWs to actuate the mirrors to correct the beamwalk.
Although effective within their operational parameters, the current state-of-the-art beamwalk maintenance systems based on active beamwalk mirrors suffer from several shortcomings. One of the problems is that the beamwalk mirror systems cannot handle large disturbances due to the limited range of movements of the mirrors and limited range of alignment operation that can be accomplished with a system of mirrors. Another problem is what is known as residual jitter. Although the feedback control systems for the beamwalk mirrors are driven by light (laser) and electronics, the system has finite, nonzero response time. This means that small beamwalks that occur before the mirror systems have a chance to respond cannot be corrected, and, as a result, beamwalk mirror systems have inherently uncorrectable residual jitter corresponding to their system response time.
Other problems are related to the complexity of the active beamwalk mirror systems. As described above, the active mirror based beamwalk maintenance systems are delicate systems with a large number of parts. As well known in system engineering arts, the larger the number of parts, the greater the frequency of system failures, resulting from the failures of one or more parts. Such comparatively high failure rate is particularly problematic for laser systems deployed in difficult-to-service environments, such as the Space Based Laser (SBL).
It can be seen, then, there is a need in the field for a simpler beamwalk maintenance system that can handle large platform disturbances and has zero residual jitter.